1. Field of the Invention
This invention relates to a method for the manufacture of a cushioning material. More particularly, the invention relates to a method for the manufacture of a cushioning material comprising a three-dimensionally crimped filament mass of synthetic fiber, which cushioning material is capable of retaining its original cushioning property intact through prolonged repeated use.
2. Description of the Prior Arts
According to the inventors' earlier discovery, a cushioning material obtained by cutting three-dimensional crimped filaments to a prescribed length, wadding the cut filaments into a mass, disentangling the filaments from the mass and at the same time compressing them into a required shape and uniting the individual adjacent filaments at the points of their mutual contact by use of an adhesive agent possesses high impact resilience, shows permeability to gas and excels in cushioning property. According to the inventors' further discovery (U.S. Pat. No. 4,172,174) a cushioning material of a construction obtained by wadding synthetic filaments containing three-dimensionally crimped filaments into a mass and uniting the individual adjacent filaments in the mass at the points of their mutual contact by use of an adhesive agent exhibits still better properties when the curls in the filaments of the cushioning material are shaped so as to acquire directionality partially and, consequently, the portions in which curled or crimped filaments assuming various shapes during their extractive and contractive deformation are allowed to entangle more densely than in other portions, are formed in the direction in which the applied load is desired to produce its impact and the portions of such concentrated entanglement are distributed in proportion to the desired load strength.
This cushioning material is manufactured by compressing a wad of three-dimensionally crimped filaments into an aggregated block of filaments of a stated bulk density by means of an endless belt and/or a roller or some other means, needling the shaped block to a stated needle density with needles each provided with barbs and, with or without a subsequent rubbing treatment, either spraying an adhesive agent downwardly onto the shaped block of filaments on an endless belt in motion in a substantially horizontal direction or immersing the shaped block of filaments in a bath of the adhesive agent and lifting it from the bath, and thereafter drying the wet block of filaments on the endless belt running in a substantially horizontal direction by heating.
Although the cushioning material manufactured by this method exhibits permeability to gas and excels in cushioning property, it has a disadvantage that it undergoes accumulation of residual strain, a phenomenon known as "collapse," after prolonged repetitive use. Further, since this cushion is deficient in surface smoothness, it gives an unpleasant sensation to a person sitting or lying thereon.
An object of this invention, therefore, is to provide a method for the manufacture of a cushioning material which suffers very little accumulation of residual strain even after prolonged repetitive use.